fix: towards torch 2.5 compatibility / fix unit tests (github actions)

[flxst]

What does this PR do?

This PR fixes the failing unit tests in the main branch. There were two problems, related to torch 2.5 and github actions.

The first problem was caused by the import of a variable that changed its name from T_co in torch 2.4 (see here) to _T_co in torch 2.5 (see here). This has been fixed in 787099d1eaa45afc2c3007a7919c431737310ec3.

The second problem concerns the installation of flash attention in conjunction with torch 2.5 which is relatively new, see e.g. here. Note that---for unknown reasons---the problem only arises in github actions, not (necessarily) in local testing. As a temporary workaround, the torch version has been pinned to 2.4.1 in da5862eca9d1cd410c9354cf374609cf3b57835d. Note that this should be undone once the problem has been fixed properly. See issue #267 for more details.

General Changes

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Breaking Changes

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Checklist before submitting final PR

• [x] My PR is minimal and addresses one issue in isolation
• [x] I have merged the latest version of the target branch into this feature branch
• [x] I have reviewed my own code w.r.t. correct implementation, missing type hints, proper documentation, etc.
• [ ] I have run a sample config for model training
• [x] I have checked that all tests run through (python tests/tests.py)
• [ ] I have updated the internal changelog (CHANGELOG_DEV.md)

[flxst]

Tests successfully run through: https://github.com/Modalities/modalities/actions/runs/11795437961/job/32855145364